Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$222.97	7.683%	$240.1008	$240.10	$240.10	$240.10
Purchase #2	$87.45	3.124%	$90.1819	$90.18	$90.20	$90.20
Purchase #3	$49.53	10.812%	$54.8852	$54.89	$54.90	$54.90
Purchase #4	$127.82	7.225%	$137.055	$137.06	$137.05	$137.10
Purchase #5	$194.95	8.496%	$211.513	$211.51	$211.50	$211.50
Purchase #6	$61.81	4.844%	$64.8041	$64.80	$64.80	$64.80
Purchase #7	$46.64	6.871%	$49.8446	$49.84	$49.85	$49.80
7 purchase totals =	$791.17		$848.3846	$848.38	$848.40	$848.40